Try to restore the old preferences, if any, if possible

Preferences were saved using jStorage. The browsers which ULS supports now
have wide native support for local storage, so we removed jquery.jStorage
in I09b2bd52972.

The old local storage key was 'jStorage' as put by jquery.jStorage. We now
check if that key is present. If so we migrate the preferences and remove
the old key to save space. We are not aware of anything else using this
module.

Change-Id: I995a32c4cb7a3bc818fe255f92dbc972211cb112

resources/js/ext.uls.preferences.js

@@ -137,6 +137,16 @@
 				// No value supplied, return value
 				try {
 					data = localStorage.getItem( key );
+					if ( !data ) {
+						// Try to restore the old preferences, if any, if possible.
+						try {
+							data = JSON.parse( localStorage.getItem( 'jStorage' ) )['uls-preferences'];
+							// And try to remove it.
+							localStorage.removeItem( 'jStorage' );
+						} catch ( e ) {
+							// Don't bother about it.
+						}
+					}
 				} catch ( e ) { // Use cookie
 					data = $.cookie( key );
 				}